1. Field of the Invention
The invention relates to flat panel displays, and more particularly to structures and methods of manufacturing field emission displays that provide for viewing of the display through the back plate, whereas the conventional method of viewing is through the front plate.
2. Description of the Related Art
In display technology, there is an increasing need for flat, thin, lightweight displays to replace the traditional cathode ray tube (CRT) device. One of several technologies that provide this capability is field emission displays (FED). An array of very small, conical emitters is formed on a back plate, typically using a semiconductor substrate as the base, and are addressed via a matrix of columns and lines. These emitters are connected at their base to a conductive cathode, and the tips of the emitters are in close proximity to and are surrounded by a second conductive surface, usually referred to as the gate. When the proper voltages are applied to the cathode and gate, electron emission occurs from the emitter tips, with the electrons attracted to a third conductive surface, the anode, formed on an opposite face plate and on which there is cathodoluminescent material that emits light when excited by the emitted electrons. The viewer of the display typically views the display image thus formed through the face plate.
FIG. 1 is a cross-sectional view of a portion of a field emission display. Row electrodes 12, also called the cathode, are formed on a baseplate 10, over a buffer layer 11, and have emitter tips 14 mounted thereon. The emitters are separated by insulating layer 16. A column electrode 18, or gate, with openings 17 for the emitter tips, is formed on the insulating layer 16 and is formed perpendicular to the row electrodes. When electrons 20 are emitted, they are attracted to transparent conductive anode 22 and upon striking phosphor 23 mounted on the anode, light is emitted. However, light 26 that is emitted in the direction of a viewer of the display, who would be looking through glass plate 24, must travel through the phosphor 23, the anode 22 and the glass 24. The luminous efficiency is reduced primarily due to absorption by the phosphor.
Workers in the art are aware of this problem and have attempted to resolve it, with one approach disclosed in U.S. Pat. No. 5,216,324 (Curtin), in which the display image is viewed through the back plate, either by forming the conductive and transparent layers on the back plate of a transparent material, or making the conductive lines very thin, both of which increase the amount of light that can be transmitted to the viewer. A drawback to the approach of using transparent conductive materials, which include indium tin oxide and the like, is reduced conductivity compared to the more commonly used metallic materials. A problem with the embodiment using very thin lines is that very few emitter tips can be formed at each pixel, which decreases the luminous efficiency, and degrades the display uniformity, stability and reliability, as compared to a display having many tips at each pixel.